Individual cylinder spark deration improves engine control computer knock routine control strategies. Previous systems measured knock or detonation of all the cylinders and averaged them over time. Any individual cylinder which was experiencing detonation had an influence as to whether the control system would derate the spark. However, the cylinders not experiencing detonation would also have an influence on the control system in the opposite manner. Strategies took all of the detonation information from each of the cylinders and treated it as an average to derate the spark, if necessary, for all of the cylinders.
In these routines, pressure is exerted against spark deration, by automatically decaying the spark advance derate value held in memory as a function of time. This forces the system to update its information to reevaluate detonation in an attempt to provide an accurate spark advance derate signal.
In the subject disclosure, the control strategy is changed to respond to the detonation which has occurred in an individual cylinder. The control strategy then determines how much spark deration should occur for each individual cylinder and fires the spark accordingly. Consequently, a more optimum spark advance is obtained so that the engine runs at a more precise knock-free ignition level.
Additional advantages by use of the subject strategy include the ability to operate the engine with lower octane fuels; the ability to correct knock in the cylinder of its source (typically one cylinder is the first to knock) which eliminates unnecessary performance and power derations which occur if all cylinders are derated in response to knock in one cylinder; and the tighter control of engine exhaust temperature which, if too high, can adversely affect component durability.